VectorNet: collaborative mapping of arthropod disease vectors in Europe and surrounding areas since 2010

Background Arthropod vectors such as ticks, mosquitoes, sandflies and biting midges are of public and veterinary health significance because of the pathogens they can transmit. Understanding their distributions is a key means of assessing risk. VectorNet maps their distribution in the EU and surrounding areas. Aim We aim to describe the methodology underlying VectorNet maps, encourage standardisation and evaluate output. Method s: Vector distribution and surveillance activity data have been collected since 2010 from a combination of literature searches, field-survey data by entomologist volunteers via a network facilitated for each participating country and expert validation. Data were collated by VectorNet members and extensively validated during data entry and mapping processes. Results As of 2021, the VectorNet archive consisted of ca 475,000 records relating to > 330 species. Maps for 42 species are routinely produced online at subnational administrative unit resolution. On VectorNet maps, there are relatively few areas where surveillance has been recorded but there are no distribution data. Comparison with other continental databases, namely the Global Biodiversity Information Facility and VectorBase show that VectorNet has 5–10 times as many records overall, although three species are better represented in the other databases. In addition, VectorNet maps show where species are absent. VectorNet’s impact as assessed by citations (ca 60 per year) and web statistics (58,000 views) is substantial and its maps are widely used as reference material by professionals and the public. Conclusion VectorNet maps are the pre-eminent source of rigorously validated arthropod vector maps for Europe and its surrounding areas.


Time limits
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Minimum data requirements for eligibility
Data Source: a personal communication without an electronic document with the relevant data is not sufficient, but an unpublished report is fine as long as it is available for access.
Location: data with a precision to less than NUTS2 level or equivalent should not be considered, data with NUTS2 precision should be marked as such.
Vector species: data where samples are not identified to the level of species or species groups, except where currently allowed in the migrated VectorNet list, should not be considered: -Exclusion if identification is not based on reliable method within species complexes (e.g. Anopheles maculipennis complex: morphology accepted only for An. sacharovi adults, molecular methods only for all other cases).
Reported status or number of specimens caught: if the number of specimens caught is not reported, the reported status is a mandatory minimum data requirement.
Collection effort end date: If the source does not have a valid vector collection end date with accuracy less than a year, the data should not be considered.

SUPPLEMENTRAY INFORMATION SECTION IV: Supplementary Table S4: Quality Indicators
Processes that ensure the quality of the database work on different levels: a) A standardised search string is created to ensure the accuracy and consistency in the literature review; b) A data entry template is created for complete, accurate and consistent data entry, and c) Entry restrictions are put in place within the data entry template to ensure valid and accurate data entry Random data quality checks on 1% of the submitted data are performed after data uploads, and the quality criteria completeness, unique-ness, validity, accuracy and consistence are checked based on quality indicators for these qualities. The Table lists the fields to be included in the QI assessment: which are evaluated together and which not. The data entry tool comes with a manual to ensure ease of use and correct use. The quality indicators are calculated after the new data entry system is implemented, tested and validated, and the backlog of data has been entered into the new system. The quality indicators are calculated from the newly migrated database and apart from uniqueness, all indicators are only calculated for the new data.

Completeness
Completeness is expressed by the number of fields that are filled in. An analysis per column are made over the database to evaluate the extracted data and the data entry template. Which fields are checked can be found in the Table below. The QI for uniqueness is the proportion of complete records, as compared to the data filled from the random quality check.

Uniqueness
Uniqueness is assessed for the following: species, coordinates, VectorLifeStage, VectorSex, CollectionPlaceID, CollectionEffortStartDate, VectorCollectionMethod, VectorHostSpecies, Host Bodypart and source as a measure for the uniqueness. A duplicate constitutes a record where all these fields are the same. If the source is different (a different document) but the rest is the same, this is not counted as a duplicate. Duplicates are marked in the database for easy filtering but are not automatically removed. The QI for uniqueness is the proportion of duplicate records.

Validity and Correctness
There are specific restrictions built into the data entry template (e.g. location data entered with a dot and not a comma etc.). The QI for validity is the proportion of valid records.

Correctness
The correctness of the data is different than validity. An entered cell can be valid according to the restrictions in the data entry template but can be not correct, e.g. the species name is correctly spelled but is the wrong species. This is checked during the data quality check, and the QI for correctness is the proportion of correct records.

Accuracy and Consistency
Accuracy and consistency of new uploads is ensured by using defined upload templates. Within the template excel file there are several limitations and lists baked in to ensure the consistency of the data upload. The QI for accuracy and consistency is the proportion of records that comply with the template lists (out of those that have pre-defined lists).  year for which active surveillance (so not including passive surveillance through Citizen Science reporting) is reported and b) surveillance effort. For each admin unit, surveillance was coded by type with the highest code reflecting the highest effort as shown on the map legend. The highest surveillance type that occurred in an administrative area during 2015-2019 is depicted, with lower type categories contributing to the effort score with a lower weight as presented in the table at the end of the commentary text. The highest type-code that occurred during the period 2015-2019 decides the colour (hue) of the admin unit. The frequency with which it occurred decides the saturation of the colour: a deeper colour indicates more frequent surveillance. If lower surveillance types also occurred in the same unit, these also contribute to the saturation, but with a lower weight than the highest code which decides the hue.
Each map also shows the weighting table in the right-hand column, interpreted as follows: Highest level Level 1 2 3 4 5 1 1 0 0 0 0 2 1 1 0.5 0.25 3 1 0.5 0.25 4 1 0.5 5 1 All Level one (citizen science) scores are unweighted or discounted if reported to include active surveillance. All other level two and three surveillance scores are unweighted. If the most intensive surveillance in a polygon is level 4 or 5, scores for the less intensively sampled periods are progressively reduced as sampling level falls.

Figures S 6, a and b
show a comparison between surveillance activities and distribution status to assess where the two match (i.e. there is surveillance and data, or where there is no surveillance and no data). A mismatch implies that either there are no data available or that the data have not been located. Comparison with GBIF records (in Brown) About half of the GBIF records are located in VectorNet polygons with no data, in particular in Benelux, Germany and Ireland. To address that, an effort in accessing grey literature and unpublished data sets for these countries is required. There are no GBIF records in VectorNet polygons defined as absent. For this species in particular, VectorNet data are under-reported considering the reported surveillance effort ( Figure S2).  Figure S22: Culicoides dewulfi Culicoides dewulfi is a species belonging to the subgenus Avaritia, with a Palearctic distribution, including northern Russia. This species has a biology and an ecology very similar to C. chiopterus. Indeed immatures develop exclusively in cattle and horse dung. Moreover, this species has been recorded feed on a variety of mammals, including ruminants, equids or also humans. Culicoides dewulfi has been implicated in the transmission of bluetongue and Schmallenberg viruses in Europe.

VN MAP MARCH 21
Culicoides dewulfi has, as C. chiopterus, a wide distribution in Europe. However, even if they are both dung-breeding species, the northern limit of C. dewulfi is at a more southern latitude than C chiopterus, as this species is absent from northern Scandinavia, whereas its southern limit is at a more southern latitude, as this species is recorded in southern Italy. There is a single record of this species in northern Africa, in the High Plains of Algeria, suggesting the presence of this species in particular environments.

Comparison with GBIF records (in Brown)
The GBIF records for C. dewulfi are located mostly in the northern part of Europe, where this species is the most abundant. Three quarters of them fall in the VectorNet polygons of presence, whereas few fall in the VectorNet polygons with no data, especially in the United Kingdom, highlighting possible unpublished datasets in this country.  Figure S23: Culicoides imicola Culicoides imicola is a species of the Avaritia subgenus. This Afrotropical species is widespread in Africa, in the Mediterranean basin and in the Middle East, and is occasionally recorded in the Far East (e.g. India). Immatures develop in a wide range of semi-aquatic habitats that are usually associated with livestock productions, in areas next to pond shorelines and irrigation channels. This adult feeds opportunistically on a wide variety of mammals including ruminants, equids, humans (rarely) and exotic host species in zoos. Culicoides imicola is a well-known vector of economically important livestock viruses such as bluetongue virus affecting domestic and wild ruminants or African horse sickness (AHS) virus affecting equids. The ability of culicoides to transmit these orbiviruses was first demonstrated in this species in the 1940s.

VN MAP MARCH 21
Culicoides imicola is widespread all around the Mediterranean Sea, including western Mediterranean islands where this species is particularly abundant. Its northern distribution limit borders the North of Portugal, crosses Spain -this species is absent in the Extremadura region, but recorded in northwestern and northeastern Spain, touches the South of the French mainland, follows the Italian Ligurian and Tyrrhenian coast and touches the southernmost part of North Macedonia and Bulgaria. The southern limit highlights the transition between the Mediterranean area and the Saharan one This species is better studied than most of the rest of the genus, and the absences better researched.

Comparison with GBIF records (in Brown)
Given the epidemiological prominence of this species, it is perhaps surprising that there are only 6 GBIF records for C. imicola. This may reflect the academic value of data on this species, which often hinders publishing data to the public domain. The 2 records falling outside VectorNet presence polygons are in Egypt, from where this species is known. No information is available up to now in the VectorNet database for this country.  Figure S41: Hyalomma marginatumCCHF Hyalomma marginatum is the primary European vector of CCHFV. Adult stages are frequently found on cattle where it has a predisposition to biting around the perineum and underbelly. They also often bite humans. The immature stages are found on birds and lagomorphs. The immature stages are nidifugous and are often carried by migratory birds to distant (northern) locations. Here, the ability of the engorged nymph to moult to the adult stage is climate dependent. This species does not quest so are normally sampled by examining the animal hosts, rather than more traditional flagging techniques used for other tick species such as Ixodes and Dermacentor. In addition, in contrast to other genera, including Ixodes, the Hyalomma ticks can survive in more arid environments, and are not restricted to humid environments, often afforded by forested habitats.

VN MAP MARCH 21
The presence records of Hyalomma marginatum are limited to the warmer climates of southern Europe and the Mediterranean. All records in more northerly locations (represented here in yellow) are records of imported ticks. They are frequently reported on migratory birds. During the heatwave summer 2018, nymphs were able to complete their temperature-dependent moult and many adults were collected in these northerly areas. However, this does not mean that they are established.
Comparison with GBIF records (in Brown) There are few records of this tick in GBIF most of which match the VectorNet distributions. Their distribution illustrates the challenge in mapping records of H. marginatum. The records in southern Europe likely represent data from established populations, and their records were probably from samples from large animal hosts. The records in the VectorNet absent areas in northern Europe, suggest that the tick is found across Europe. However, it is more likely that these are imported ticks and do not constitute established populations.  Figure S42: Ixodes persulcatus Ixodes persulcatus is very similar morphologically to Ixodes ricinus, as it occurs in similar woodland habitats though it is found in more grassy areas. Its populations tend to peak earlier in the year. It is also a vector of Borrelia burgdorferi s.l. and TBEV, along with other tick-borne pathogens such as Anaplasma.

VN MAP MARCH 21
This tick species has a restricted distribution in western Russia, Finland and the Baltics states. It is likely that its morphological and habitat similarities to I. ricinus might make it under-recorded in fringe areas. It was recently detected in northern Sweden.

Comparison with GBIF records (in Brown)
Most of the GBIF records match the VectorNet presence reports or occur within the inferable distributional range of VectorNet records. The intensity of recording in western Russia/Finland is indicative of its main range.  Figure S43: Ixodes Ricinus Ixodes ricinus is widespread across Europe. Principally a tick of habitats that afford a moist microclimate like forests, it is found in grazed grasslands, moorland/heathland/montane habitats, mosaic habitats with agriculture, grassland and pasture, as well as urban parks. It's ubiquity and wide host range makes it an ideal vector for several pathogens. Larvae, nymphs and adults can be found on a wide range of animal host. Humans are often bitten, as are companion animals such as dogs and cats, and so records of tick bites from these species are numerous. In more sylvatic habitats, all stages of tick can be found on large ungulates such as deer, cattle and sheep, with the immature tick stages infesting a range of small and medium sized mammals and birds. It is the primary vector of Borrelia burgdorferi (the causative agent of Lyme borreliosis), Tick-borne encephalitis virus and other pathogens such as Babesia, Anaplasma, Borrelia miyamotoi, Ricketssia and Louping ill virus.

VN MAP MARCH 21
The distribution is essentially panregional, but acquired records are biased to west central and southern areas, with relatively few data records from eastern regions, so extrapolations are likely to be less accurate to east. Records of introduction (yellow) are seen in the far north of its range. There are few absence records.
Ixodes ricinus is limited in its distribution where there is an absence of hosts or a microclimate that limits their survival. For example, southern parts of Europe are too dry for their survival. High altitude areas of the Alps of central Europe are too cold for their survival, although they are being found at high altitude. In northern regions, there is a climatic limit, but the absence of abundant hosts is a limiting factor in places like Iceland.
This species is one of the most prolifically recorded by GBIF. Ninety percent of the GBIF occurrences are in VectorNet areas defined as present with about ten percent in areas with No Data, most noticeably in Norway and to a lesser extent in Russia and the Baltic countries.
There are no GBIF records in VectorNet polygons defined as absent.
Ixodes ricinus remains one of the best recorded species of tick in Europe. For some records in southern Europe, these are now being questioned as other similar species (I. gibbosus. I. inopinatus).

GBIF Present VN Present VN Absent VN No Data Total
No 579  The Ornithodorus erraticus complex includes a number of similar species and is a subject of much debate. They are associated with warm blooded animals, such as ungulates, carnivores, rodents and insectivores. Species of the O. erraticus complex are often found on pigs, with some experimental evidence of a role in the transmission of African swine fever virus.

VN MAP MARCH 21
There is little published data on the distribution of these ticks, and they are generally under-recorded. The species of wider Ornithodoros genus are also not widely recorded as many are specialist species of wildlife and livestock, including some species associated with seabirds. Unlike the Ixodidae that spend time in vegetation, questing for a host, these species tend to be more nidicolous and therefore are not easily collected during routine tick sampling.

Comparison with GBIF records (in Brown)
There are no GBIF Records. The lack of data is indicative of the paucity of records of O. erraticus.